FIG. 4 is a block diagram of main portions of a conventional CAT scanner. This scanner includes an x-ray tube 20 for producing x-rays which are shaped into a sectorial form by a collimator 21 so as to match x-ray detectors 22. An object 23 that is to be examined is inserted in a hole 24. A high-voltage generator portion 25 produces a high voltage that is supplied to the x-ray tube. The rotary portion and the stationary portion of the scanner are indicated by numerals 28 and 29, respectively. The x-ray tube 20, the collimator 21, the x-ray detectors 22, and a data acquisition portion 27 are mounted on the rotary portion 28. The electric power from the high-voltage generator portion 25 is supplied to the x-ray tube 20 on the rotary portion 28 via a slip ring (not shown). In the past, the high voltage that is to be supplied to the tube 20 has been passed through the slip ring. Therefore, the slip ring has required a special insulating material such as an insulating oil or insulating gas.
There exists an improvement over the aforementioned conventional scanner. Specifically, in this improved scanner, a line voltage is directly rectified to produce a DC voltage which is supplied via a slip ring to a high voltage generator mounted on a rotary portion similar to the rotary portion 28 shown in FIG. 4. The high voltage produced by the high voltage generator is supplied to an x-ray tube. The high voltage generator is a DC--DC converter and uses a chopper, for example, to convert its input DC voltage into an RF AC voltage which is then stepped up by a transformer. The AC voltage is doubled and rectified to obtain a high DC voltage. When this method is used, it is only necessary that the slip ring resist a low voltage. Therefore, no special insulating mechanism is needed. However, the mounted DC--DC converter increases the weight of the rotary portion.